1. Technical Field
The present invention relates in general to electric motors and, in particular, to a reduced voltage controller for operating a motor.
2. Background Art
As is well-known in the art, motor speed controllers can use a DC bus voltage supplied to one or more half bridges which are, in turn connected to the appropriate windings of a motor to control the motor speed. These half bridges switch between the top component (usually a power FET or IGBT) and the bottom. Where the top component is switched between the DC bus and ground, the output of the half bridge switches between full supply and zero volts. To minimize the audible noise, any switching of these components generally occurs above 20 kHz. The end result of switching these half bridges generates a sinusoidal wave, which is ideal to run an AC motor.
In the design of these motor systems, it is generally desirable to maximize motor and controller efficiency. One potential inefficiency is caused by the resistive heating of the electric components in the system, including in the controller output stage, as well as the windings of the controller motor. These losses are approximately equal to I.sup.2 R. As can be seen, the heat losses are only directly proportional to the resistance in the circuit, yet proportional to the square of the current through the circuit.
Accordingly, it is an object of the present invention to minimize heat losses in a motor controller by lowering the current through the controller and associated motor.
It is an associated object of the present invention to minimize the amount of heat sinking required in such a controller, which, in turn, will lower the overall controller cost.
These and other objects of the present invention will become apparent to those of ordinary skill in the art in light of the present specification, drawings and claims.